Rasmussen syndrome is a constellation of symptons of unexplained onset, consisting of intractable focal motor seizures. The immune mediated inflammatory process of Rasmussen's syndrome can be stopped by immunoablation with high dose cyclosphosphamide. Our aim is to treat Rasmussen's syndrom with a high dose cyclophosphamide resulting in peripheral immunoablation. This will hopefully lead to an arrest of the central nervous system inflammatory process that is the hallmark of this disease. If the remission is durable, children could then be spared the morbidity associated with a hemispherectomy. This protocol would provide pilot data for submission of a larger grant to investigate this therapy more fully.